Which laboratory finding confirms that clear rhinorrhoea draining from the nose after endoscopic sinus surgery is cerebrospinal fluid?

• A Glucose concentration greater than 60 mg/dL
• B Protein concentration less than 15 mg/dL
• C Positive Gram stain showing diplococci
• D Presence of beta-2 transferrin on electrophoresis ✓

Explanation

Beta-2 transferrin is present only in cerebrospinal fluid, perilymph, and aqueous humour, so its detection by electrophoresis or immunofixation is the definitive confirmatory test for a CSF leak. Glucose testing with dipsticks gives false positives from nasal secretions and tears, since normal nasal mucus contains reducing sugars. Protein levels are supportive but not specific, and Gram stain addresses infection rather than leak identification.

Reference: Scott-Brown's Essential Otorhinolaryngology, 3rd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.